Download Approaches Expectations

Course: Biology
Grade Level: 9-10
Type: Informational/Explanatory
Structure: Description
Teaching Task 12: How does the structure of a cell membrane allow a cell to perform both active
and passive transport? After reading informational texts, write an essay that defines and describes
the fluid mosaic model and explains how molecules are transported through a cell membrane using
various methods of active and passive transport. Support your discussion with evidence from the
text(s). (L2): What conclusions or implications can you draw?
Performance Level: Approaches Expectations
The cell membrane is not one solid piece, it has tiny holes allowing entrance and exit to the
cell. The cell membrane extends around the outside of a cell inside the cell wall. Understanding the
cell membrane, passive transport, and active transport is how you gain knowledge about the
structure and function of a cell membrane.
Around cells there are cell membranes surrounding it. Cell membranes are selectively
permeable. Which means it allows some molecules to pass through it easily and others have a
harder time or can not pass. (Cellular Transport, n.d.) Size and polarity will prevent molecules from
passing through the membrane. (Cellular Transport, n.d.) Vibrations of the membrane allow small
water molecules to pass, and larger molecules pass less easily. (Cellular Transport, n.d.) For
example, diffusion moves small particles back and forth across the membrane based on the
concentration of a solutions (high to low). Cholesterol is required to help maintain the condition of
a cell membrane. The cell membrane contains a lipid bilayer, carbohydrate chains, and proteins.
The lipid bilayer has a hydrophilic head (water loving), and a hydrophobic tail (water fearing),
which also means the lipid bilayer is amphipathic. (Cellular Transport, n.d.) Proteins and
phospholipids are what make up most of the cell membrane. The proteins generally float in the
bilayer. There is also a protein pump in the membrane that allows for passing of molecules.
(Cellular Transport, n.d.) Carbohydrate chains act as “Identification Tags” so other cells know that
it belongs there. (Cellular Transport, n.d.) The membrane is called a fluid mosaic model due to all
the components that make it up. (Cellular Transport, n.d.) Part of the cell membrane is the way
molecules get transported across of it through forms of passive and active transport.
There are two types of transportation of molecules which are passive and active. The
difference between them is that active uses energy and passive does not. During either transport
there can be different concentration gradients between different solutions. (Cellular Transport, n.d.).
One example of passive transport is diffusion, when molecules move from high to low
concentration. (Cellular Transport, n.d.) More specifically there is facilitated diffusion that uses a
protein channel that makes it easier for molecules to pass. (Cellular Transport, n.d.) Another
example is osmosis which is the passing of water molecules through a cell and its membrane.
Isotonic, hypotonic, and hypertonic are three different ways of comparing two solutions. (Cellular
Transport, n.d.) For isotonic it means when in comparison the concentration of two solutions are
exactly the same. Hypotonic is when comparing two you take the solution with a lower
concentration. Hypertonic is the opposite of hypotonic where you take the one with a higher
concentration. (Cellular Transport, n.d.) The other form of transport is called Active transport
which moves from lower concentration to higher concentration (Miller & Levine, 2012, pgs 204213) ATP is the type of energy used in active transport. (Miller & Levine, 2012, pgs 204-213)
To pass molecules through it uses a protein pump. (Miller & Levine, 2012, pgs 204-213)
Endocytosis is when a cell takes in content through a vacuole. Exocytosis is when a cell releases
contents through the vacuole. When a cell “eats” and takes in larger molecules it’s called
phagocytosis. (Miller & Levine, 2012, pgs 204-213) Pinocytosis is the entering of liquids into a cell
by small vesicles created in the membrane. Passive and active transport are important aspects of
knowing about cell membranes.
The cell membrane monitors what enters and exits a cell. Due to it being selectively
permeable it allows molecules to move across it with passive or active transport. Understanding the
structure and function of a cell membrane starts with having knowledge about the cell membrane,
passive transport, and active transport.
Annotation
Focus
2
Reading/Research 2.5
Controlling Idea
2.5
Development
2
Organization
2
Conventions
1.5
Content
Understanding
2
The essay addresses most aspects of the prompt with an uneven focus
when the writer explains the cellular transport process. The details
regarding the fluid mosaic model and all forms of cellular transport are
weak.
The writer presents limited information which relies on only two
sources. Addressing the credibility of all information would strengthen
the essay.
The thesis generally establishes the task as related to cell membrane
structure and function, but it is unevenly maintained throughout the
essay: Understanding the cell membrane, passive transport, and active
transport is how you gain knowledge about the structure and function
of a cell membrane.
The writer provides limited, appropriate details to support cell
membrane structure and molecular transport but does not describe the
model’s relationship to cellular transport. The writer could strengthen
the development of the essay by expanding the depth of specific
scientific vocabulary and integrating details into the cellular transport
processes: The membrane is called a fluid mosaic model due to all the
components that make it up.
The essay attempts to use an appropriate organizational structure, but
the flow of paragraphs is awkward. For example, the transition from
explaining diffusion to the role of cholesterol in the cell membrane
should be separated. The writer could create cohesion through
enhanced transitions and compartmentalization of specific concepts
within the topic of cellular transport.
The writer demonstrates a minimal command of standard English
conventions and scientific vocabulary. Sources are used without
citation. The essay would benefit from academic language that reflects
a formal tone (e.g., “…how you gain knowledge about…”, “…where
you take the one with…”, and “…when a cell ‘eats’…”). The writer
needs appropriate citations and bibliography to avoid plagiarism.
The writer demonstrates a limited understanding with explanations that
lack detail and insights of the biological and chemical concepts related
to membrane structure, function, and transport. Minor errors exist in
the explanation of cellular transport: “Passive and active transport are
important are important aspects of knowing about cell membranes.”
This student would benefit from feedback, discussion, and/or instruction in the following
areas:
•
A more thorough understanding of scientific terminology relating to cell membranes and
cell transport.
•
Complete integration of the Fluid Mosaic Model within cellular transport.
•
Complete development of the controlling idea to include all aspects of the prompt.
•
Consistent and appropriate use of parenthetical citations and bibliography is required.